LEVEL: A computer program for solving the radial Schrödinger equation for bound and quasibound levels

•Efficient computer program for solving the radial or 1D Schroedinger equation.•Automatically finds quasibound levels & calculates their widths (tunneling lifetimes).•Can find all bound vibrational levels if any single-or double-minimum potential well.•Can input and use potentials having a several analytic forms. or pointwise potential.•Can incorporate with atomic-mass-dependent Born-Oppeheimer breakdown corrections.•Calculates Bv and the first six centrifugal distortion constants for any/all levels.•Calculates expectation values of various radial variables and of functions of them.•For two potential functions, can generate line lists, FCFs and matrix elements.

This paper describes program LEVEL, which can solve the radial or one-dimensional Schrödinger equation and automatically locate either all of, or a selected number of, the bound and/or quasibound levels of any smooth single- or double-minimum potential, and calculate inertial rotation and centrifugal distortion constants and various expectation values for those levels. It can also calculate Franck-Condon factors and other off-diagonal matrix elements, either between levels of a single potential or between levels of two different potentials. The potential energy function may be defined by any one of a number of analytic functions, or by a set of input potential function values which the code will interpolate over and extrapolate beyond to span the desired range.